One of the most frequently asked questions to arise when people attend Pro Silva Ireland forest visits is “What about stability?”
One of the few even aged conifer plantations in Slovenia was blown down in just 10 minutes.
People have seen the damage that the strong Atlantic winds can cause to a conifer plantation but we have nothing else to compare against this because the only commercial ‘forests’ we have here are conifer plantations.
But stop to think about it. The remnant old growth forests are in the ‘ancient’ category. That is, they’ve been here a long time. Therefore they didn’t blow over during their long lives in the strong Atlantic winds. Although ancient woodlands cover only about 1% of the country, we all know this has nothing to do with strong winds.
So how come remnant strip woodlands in the hedgerows and this scattering of old growth forests didn’t blow over? The answer, – because they have achieved the knack of stability. Here’s a good example to illustrate how that works:
My good friends Cathy Fitzgerald and her husband Martin were making a roadway through their spruce and alder forest last year. Martin cut down the trees with his chainsaw then came back with a mini digger and uprooted the stumps. No problem with the spruce. The roots were shallow and flat and lifted out with ease.
The shallow and flat root system of spruce doesn't grip the earth well on its own.
However the alder were a different matter. Their strong tap roots anchored them deep into the ground. No amount of work with the mini digger could shift them. Martin had to dig around their base with a pick and cut through the root with the saw.
So this shows us one amazing yet simple strategy employed in a natural forest to effect its own stability against strong winds. Some species’ roots balance on the surface and others serve the purpose of fastening down the forest so it can stand up to the ravages of time.
To achieve an irregular forest system from a regular spruce plantation, thinning is vital and needs to be approached in a different way.
In regular forestry the aim is to end up with all big trees of the same size. But when we consult with nature we find that this is not the way to make a forest to last. Natures forests are made up of trees of all sizes and of many species. Everything looks chaotic and irregular. Yet somehow it works. They don’t blow down.
To follow nature’s method is not to try to replicate an old growth forest. Rather it is to use the principles nature employs to achieve this stability. Allow the native species to come in that will help to stabilize the forest. Thin to keep a mixture of both large trees and smaller ones. Favour species diversity. Avoid regular spacing throughout the forest by not having that as the focus. Suffer the early wind damage that may occur during the transformation stage, – it’s not a disaster and once the forest is truly established wind damage ceases to be such a problem.
Willem Pleines from Pro Silva Switzerland stands in the centre of a windthrow gap. The same storm took out 50% of even aged forest in this area, yet this small gap is the only damage that occurred in this close-to-nature forest. Freudenstadt, Black Forest, Germany.
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Tags: Stability
